Many excipients are sterilized by exposure to radiation before use in beneficial agent formulations. In certain types of excipients, including stearic acid and fatty acids, such irradiation produces free radicals, and peroxides. In the presence of beneficial agents which are susceptible to oxidation, such as amino acid sequences, lipids, DNA, and certain drugs, these free radicals and peroxides can oxidize the beneficial agents, thereby reducing the efficacy of the beneficial agent.
For example, when contacted by free radicals and peroxides, peptides and proteins are subject to a wide range of undesirable effects, such as sulfur oxidation, deleterious effects on carbonyls, crosslinking, hydroperoxy derivative formation, deamination, chloroamine formation, interconversions (i.e., His to Asn, Pro to HO-Pro), adduct formation (lipid peroxidation, amino acid oxidation, glycoxidation), aggregation, and peptide bond cleavage. This can lead to loss of activity, function, abnormal cellular uptake, modified gene transcription, or increased immunogenicity.
In the past, antioxidants and other free radical scavengers have been added to prevent undesirable reactions. For example, U.S. Pat. No. 6,423,351 discloses prevention of drug oxidation using a ferrous ion source. Antioxidants commonly employed in beneficial agent formulations include vitamin E, vitamin C, butylated hydroxytoluene, and butylated hydroxyanisole. However, this strategy has not always proved successful, and in all instances increases materials' costs for manufacturing the formulations.
It has now been discovered that introduction of an annealing step into the creation of drug formulations eliminates the need for scavengers, thus reducing the number of materials required to manufacture the formulations, and creating new compositions and methods for preventing oxidation of beneficial agents. Moreover, the present invention allows for protection from oxidation of beneficial agents in situations where the use of scavengers would be unsuitable.